One of the most important factors in the feasibility of precast structural modules is the weight of the modules and in particular, the weight per square foot. In this regard, structural modules refers, in general, to modules which form all or a part of a weight-bearing wall, floor/ceiling or similar structure.
It has been known to provide structural modules with a "waffle" configuration in which relatively thick "rib" components form a framework and panel portions extend between the ribs. In many configurations, particularly where structural or load-bearing modules are involved, metallic mesh or reinforcing bars (rebar) typically steel bars, were provided extending through at least a portion of the panel sections. Because of the potential for corrosion and/or rusting of the reinforcing bars and/or the potential for deterioration of the concrete adjacent the reinforcing bars, such configurations typically required a minimum of one inch or more "cover" i.e. such that steel reinforcing bars were spaced at least about one inch from any major surface of the module. In previous devices, this meant that the panel thickness was often a minimum of three inches and typically more, leading to relatively high weight per square foot. Accordingly, it would be useful to provide a precast concrete structural module which is relatively low in weight per square foot yet provides sufficient cover to any reinforcement in the panels.
To achieve the desired stiffness of the framework defined by the rib portions, the panel portions are typically required to bear an amount of tension. Because concrete, alone, is much more tolerant of compression than tension, it would be advantageous to provide a module having panels configured to withstand substantial tension without having so much panel thickness that the overall panel weight is undesirable.
The relatively large weight per square foot of previous modules has resulted in relatively high expense arising not only from the amount of materials needed for fabrication, but also the cost of transporting and erecting the modules. Module weight also placed effective limits on the height of structures, such as stacked modules, e.g. due to limitations on the total weight carried by the lowermost modules. Furthermore, there is substantial fabrication labor expense that can arise from efforts needed to position, design and construct molds, and the materials and labor costs involved in providing and placing reinforcement materials. Accordingly, it would be useful to provide a system for modular construction which is relatively light, can be readily stacked to heights greater than in previous configurations and, preferably, inexpensive to design and use.
In many situations, panels or modules are situated in locations where it is desirable to have openings therethrough to accommodate cables, pipes and the like. In some previous approaches, panels were required to be specially designed and cast so as to include any necessary openings, requiring careful planning and design and increasing costs due to the special, non-standard configuration of such panels. In other approaches, panels were cast without such openings and the openings were formed after casting e.g. by drilling or similar procedures. Such post-casting procedures as drilling, particularly through the relatively thick and/or steel-reinforced panels as described above, was a relatively labor-intensive and expensive process. In many processes for creating openings, there was a relatively high potential for cracking or splitting of a panel or module. Accordingly, it would be useful to provide a module which can be easily provided with openings in desired locations, preferably in the field, with reduced potential for cracking or splitting.